# Lesson 15: Current Induction and Lenz`s Law

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### Part 1: Current Induction

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Oersted: !

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Ways of generating current: !

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1) Move a magnet near a wire !

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2) Move a wire in a magnetic field !

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The electric generator !

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### Part 2: Lenz’s Law

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When a magnetic field is moved near a wire, the induced current in the wire will be in a direction such that row electromagnet it forms will repel the movement of

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the original magnet that produced it. !

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Example:

Draw the direction of the induced current in the solenoid !

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Example: Draw the direction of the induced current in the solenoid !

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Example: Draw the direction of the induced current in the solenoid !

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Example: Draw the direction of the induced current in the solenoid !

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Summary of Lenz’s Law !

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### Practice Problems:

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For each situation below, determine the polarity of the induced magnetic field and the direction of induced electron flow for each of the following cases. Indicate which end of the “generator” becomes a negative terminal in each case.

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In the following diagram, a metallic conductor is moved along a set of conducting rails across a magnetic field. Which end of the conductor becomes the negative terminal? In which direction does conventional current flow in the circuit?

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A bar magnet inserted into a coil of 500 turns produces an induced potential of 1.5 V,

Determine the potential difference induced when each of the following changes are made. Consider each change separately.

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A 250 turn coil is used. (0.75 V) !

The bar magnet is moved twice as fast. (3.0 V) !

Three identical magnets are inserted at once, side by side. (4.5 V)

All three of the above changes occur together. (4.5 V) !

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4.

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Where does the electrical energy of the induced current and potential difference come from?

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What form of energy provides the work for the electrical energy being made?

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A positively charged sphere is suspended between two large metal plates as shown in the diagram. A wire is placed between the poles of a horseshoe magnet and connected to the metal plates. When the wire is drawn horizontally to the right the charged ball is observed to swing toward the right-hand metal plate.

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a) !

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Determine the direction of the induced electron flow in the wire in the horseshoe magnet.

Explain.

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Is the top pole of the magnet a north pole or a south pole? Explain.

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